Recuperative radiant tube burner mechanism



March 5, 1963 F. S. BLOOM ET AL RECUPERATIVE RADIANT TUBE BURNERMECHANISM Filed June 27, 1960 2 Sheets-Sheet 1 FPE'DEP/CK 6. 54.00/14POLZAWD LHOFFMA/V ZZe/r ATTORNEYS INVENTORS I March 5, 1963 F. s. BLOOMETAL RECUPERATIVE RADIANT TUBE BURNER MECHANISM Filed June 27, 1960 2Sheets-Sheet 2 km -illl E N mwn W m EOM O VLF W A 6 M r a e E a am 5 Y Bm Q7 Q/Kkb 1M1 United rates Patent Ghice Fatented Mar. 5, 1%53 EJ379519REQUPERATHVE RADZAI-ZT TUBE BURNER MECHANEM Frederick 5. Bloom andlioiland lb. Hofiman, Mount Lebanon Township, Allegheny Count Pa; said{infiman assignor to Bloom Engineering Qonnpany, the,

Pittsburgh, Pa, a corporation of Pennsylvania Filed June 27, 1%9, Ser.No. 39,048 7 Claims. (Cl. 126-91} This invention relates to recuperativeburner constructions of the U-tube, W-tube or similar radiant tube classfor continuous or batch furnaces or other heating purposes. Moreparticularly, our invention pertains to a recuperative radiant tubeburner having a pairof legs extending through the wall of a furnace orother enclosure with burner and heat exchange elements therein incoaxial relation to such radiant tube legs and with at least therecuperator element extending into the opening through such wall.

Embodiments of this invention provide recuperative heating of thecombustion air with radiant tubes of the return bend class, such asU-tubes or W-tubes, for use on a tower furnace, in a batch annealingfurnace, or in other heating equipment, irrespective of the relativedistance between centers of the parallel legs of the tube and thethickness of the wall of such furnace or other enclosure. Moreover,recuperative constructions of this invention can be installed withmarked economy of material and labor. Further, varying distances betweenrespective radiant tubes can be accommodated with relative ease fordifierent heating specifications without detrimental clutter, ormaterial change in tube unit piping and installation expense. Stillfurther, in this invention, the recuperative heat exchange capacity of aunit can be selected for the particular service in which the embodimentis to be used.

Other objects, features and advantages of this invention will beapparent from the following description and the accompanying rawings,which are illustrative only, in which FIGURE 1 is a longitudinal sectionof a recuperative radiant tube burner mechanism embodiment of thisinvention taken along line II of FIGURE 2;

FIGURE 2 is a view, partly in section, taken along line iii-11 of FIGURE1;

FIGURE 3 is a view in plan taken along line IIIIH of FIGURE 1 with thehot air pipe removed;

FIGURE 4 is a detail view of the seal at t .e top of the hot air pipe inthe embodiment shown in the preceding figures;

FIGURE 5 is a longitudinal section, similar to that taken in FIGURE 1,of another unit embodiment of this invention; and

FIGURE 6 is a front view of the mechanism embodiment shown in FIGURE 5.

Referring to FIGURES 1 to 4 of the drawings, a re cu erative radianttube burner mechanism 10 is illustrated therein mounted in the wall 11of a tower furnace 12, or other furnace or heat enclosure. Wall 11 maybe a side, bottom or roof portion of the furnace or other enclosure and,as shown, comprises heat insulating refractory 13 within a metal shell14 to which burner mechanism it) is aifixed. Wall 11 has openings 15 and15 respectively for passage therethrough of an inlet leg 17 and anoutlet leg 13 of a conventional W- be 19, the distance between centersof which legs determine the distance between centers of the openings 25and 16. Tube 19 may be a v i-tube or a U-tube or a radiant tube ofanother shape in the return bend class having two legs requiring a pairof passages through the furnace enclosure utilizing the same. Such tubesare made generally of alloy steel to withstand eating to relatively hightemperatures to provide the thermal head in furnace 13 desired for theheat treatment of the work material, usually metal, within the furnace.

Such a wall 11 in a higher temperature furnace may have considerablethickness, the length of which thickness is utilized in the illustratedpractice of this invention. fire outer ends of legs 17 and 18 arethreaded and provided with flanges 2t and 21, respectively, aflixedthereto by means of such threads. Flanges 26 and 21 are provided withbolt holes for stud bolts, the heads of which are fixed to the furnacestructure and project out wardly therefrom in registry with such boltholes. Outwardly of the respective flanges, there is a burner sleeve 22and an exchanger sleeve 23 with respective flanges 24 and 25 having boltholes therein in registry with the bolt holes in flanges 25* and 21 sothat when nuts 26 and 27 engage the ends of the aforesaid studs, therecuperative burner mechanism is mounted in place on and in the furnace12. Preferably, gasket material is interposed between the adjoiningfaces of the respective flanges and between the tube flanges and shell14. Shell 14 is provided with openings 23 and 29 through which thereturn tube legs extend, as shown.

Sleeve 22 is provided with an annular cover 3% having a central opening31 which is tapped from opposite sides and a pilot opening 32. A pilotlight burner 33 extends through opening 32 and is held in adjustedlighting position by a thumb screw 34. A small combustible mixturestream of gas is fed through the center of burner 33 and burnsconstantly to ignite fuel from a main burner 35, positioned coaxiallywith inlet leg 17, whenever burner 35 is turned on. A pipe 36 suppliesfuel gas, or atomized fuel oil emulsion, to the interior of a fuel tubein burner 35 which leads to and is discharged at the end thereof througha flanged nozzle 37, the burner 35 being ignited by the pilot lightburner whenever the fuel supply to tube 35 is turned on. Usually thefuel supply to such a main burner 35 comes from a fuel gas manifoldwhich supplies a plurality of such radiant tube burners mounted on onefurnace or on more than one furnace to be operated in concert.

Sleeve 22 is provided with a refractory lining 38 and cover 3% has aninsulating lining 3% on its inner face. A side opening 49 extendsthrough sleeve 22 and the lining thereof to accommodate the upper end ofa hot air pipe 41 supplying the combustion air at elevated temperaturearound the fuel tube of burner 35 to combust with the fuel gas issuingfrom nozzle 37. The fuel flow rates and combustion air flow rates may becorrelated or left relatively independent depending upon the controlsystem employed for such burners, the fuel being turned down when theburner is to operate at reduced capacity with or without, as desired, acorresponding reduction in the flow of combustion air. Pipe 41 issurrounded by refractory insulation 42 in the form either of preformedor castable lagging to inhibit loss of heat and promote personnelsafety.

Exchanger sleeve 23 is lined with refractory insulation 43 and isprovided with a side opening 44 for the passage therethrough of thelower end of pipe 4-1. An inner heat exchange in the form of tube 45having a closed end 46 is positioned coaxially relative to the axis ofreturn leg 18 and extends through the sleeve 23 into the outer end ofleg 18. The inner end of tube 45 terminates in wall 3.1 and hence doesnot take away from the heating effect of the portion of leg 18 inwardlyof the inner face of that wall. Heat exchanger tube 45 is laterallyspaced from the inside of leg 18 and of sleeve 23 to provide an annularpassage 47 for gases being exhausted from radiant tube 19, such gasesyielding heat to the outside of exchanger 45 and end 46 for'transmissiontherethrough to the incoming combustion air which after heat exchangepasses as hot air through pipe 41 to the outside of burner 35. Thecooled exhaust gases are discharged through aside opening opening 48 insleeve 23 and pass to an outlet pipe 49 having a refractory lining,which outlet pipe may be connected to an eductor or fan, or both, tosend such exhaust gases on to the stack or flue that is used for thedischarge of Waste gases.

The suction in conduit 49 is also operative to aspirate combustion airthrough an inlet air pipe 56 which extends longitudinally withinexchanger 45 and terminates at 51 outwardly of end 45. Preferably,longitudinally extending, radial heat exchange fins 52 are provided onthe inner surface of exchanger 45 to aid in transmitting heat from theexhaust gases to the incoming combustion air. Such combustion air flowsthrough the interior of pipe 50, makes a return bend at the inner endand flows through the annular space 52a past fins 52 before enteringpipe 41 through a side opening 53 in exchanger 45. The outer end ofexchanger 45 may be welded to a flange 54 while the outer end of airinlet pipe so may be welded to an annular cover plate 55, such flangeand cover plate having registered' bolt openings therethrough' fo'raflixation thereof to the outer end'ofsleeve 23.

I Side opening 53 is provided with a cylindrical flange 56' and has anannular shoulder 57 against which th lower end of pipe 41 may rest. Asshown in detail FIGURE 4, pipe 41 is peripherally recessed at its upperand lower ends for a labyrinthine wire seal 58 which may consist of afew spiraling turns of wire in the recess where it may be held by tackwelding or brazing. The wire turns project slightly beyond the outsidediameter of pipe 41 enough to substantially close the space to theopposed cylindrical inside surface of flange 56 and of opening 40, withthe result that in operation, at ele-' vated temperatures, the wireturns expand and efiectively form a labyrinthine seal against the flowof gases therethrough. Moreover, such pipe 41 may be assembled inposition by axial sliding movements relative to openings 40 and 53,thereby dispensnig with threaded or union joints. A collar 59 on pipe 41may also be provided around the top of opening 53 to'inhibit exhaust gasleakage through opening 44 around the outside of pipe 41. At otherplaces, such as the faces of flanges and covers, suitable gasketing ispreferably employed.

In operation, the radiant tube burner mechanism utilizes the high heatcontent of the waste gases exiting through return leg 18 in arecuperativemanner by transferring asmuch as possible of that heatcontent through walls of the recuperator tube 45 to the incomingcombustion air passing through air inlet 50. Simultaneously, such actionreduces the quantity of heat that would otherwise pass into wall 11. Theheated combustion air flows out of the lower portion of device 10upwardly through insulated pipe 41 and into sleeve 22 and inlet leg 17of radiant tube 19 around the main fuel tube of burner 35 for theachievement in the portion of radiant tube 19 within furnace 12 ofmaximum heating temperature for the fuel rate used at the time being.Additionally, inas much as the recuperator and burner elements are incoaxial position relative to the axes of the inlet and outlet legs ofthe radiant tube, respectively, those legs can be very close togetherwithout impairing the recuperative heat exchange action. Still further,the piping connection between recuperator and burner portions of device10 is relatively simple and inexpensive; it can be made quickly and doesnot clutter the outside of the furnace or other heating enclosure towhich the device is applied. Moreover, although the embodimentsillustrated operate as a suction system under induced draft, they areequally operable as a pressure system pursuant to which a blower wouldbe connected in advance of the inlet of the air inlettu-be 50 as asubstitute for, or supplement to, the suction equipment connected tooutlet pipe 49. 1

In the modified embodiment illustrated in FIGURES 5 and 6, parts thereofcorresponding in construction and functioning to parts in the precedingembodiment, are provided with the same reference numerals, respectively,with the addition of a prime accent thereto. The modified embodimentillustrates a practice of the invention on, for example, a relativelyhigher heat exchange capacity, relatively smaller center-to-centerdistance ,L I- tube unit having the inlet and outlet legs 17' and 18'close together. The relatively higher heat exchange is obtained byextending the recuperative element longitudinally outwardly, as shown,for a greater distance for the incoming combustion air. Such length andheat exchange capacity of'the recuperative .portion of mechanism 10 canbe selectively varied in advance for the service demand for theparticular unit. As shown, the pipe 4'1 remains a simple pipingoperation still relatively free of clutter in that the upper portion41aand the" lower portion 41'!) are elbows having flanges at the meetingjoint for bolted completion of the connection. It thus will be seen thatthe invention is flexible in prac-' tice to accommodate different sizesand capacities of return bend radiant tubes and service sev'erities',with retention of advantages enumeratedabove.

Various modifications may be made in, portions of the illustratedembodiments and other embodiments provided without departing from thespirit of our invention or the scope of the appended claims.

We claim:

1. A recuperative radiant tube burner mechanism an a furnace or thelike, comprising, in combination, a return bend radiant tube having aninlet, leg and an outlet leg having portions adapted to extend inrespective passages through a wall of a furnace or the like, a burnerhaving an axially extending fuel tube, mounting means to mount said fueltube on a furnace or the like wtih said fuel tube in coaxial positionrelativeto the inlet leg of the return bend radiant tube, said mountingmeans adapted to hold the inner end' of said burner so as to terminatesubstan-f tially within the thickness of a' wall of a furnace or thelike, said fuel tube being radially spaced by said first named mountingmeans from the inside of said inlet. leg to provide a heated combustionair space around said fuel tube leading into said inletleg, an axiallyex tending recuperator having an inlet and' an outlet for combustionair, mounting means to mount said recupera tor on a furnace or the likewith said recuperator in co axial position relative'to the outlet leg'ofsaid return bend radiant tube, said last-mentioned mounting meansadapted to hold the inner end of saidrecuperator substantially Withinthat portion of said outlet leg adapted to be within the thickness of awall of a furnace or the like, said recuperator being radially spaced bysaid last-mentioned mounting means from the inside of said outlet leg toprovide an exhaust gas space around said recuperator at least withinsaid outlet leg, means for conducting exhaust gases from said outlet legaxially past and outside said recuperator in heat exchange relationtherewith, and pipe means connecting the combustion air outlet in saidrecuperator with the combustion air space around said fuel tube.

2. A recupe'rative radiant tube burner mechanism as set forth in claim 1in which said pipe means are peripherally recessed adjacent the endsthereof, said respective mounting means having cylindrically opposedportions surrounding said recesses in assembled position and expandablewire turns are provided substantially filling the space between thebottom of said recesses and said opposed portions, said who turns beingadapted to expand in use to overfill said space and form a relativelygas-tight seal.

3. A recuperative radiant tube burner mechanism for a furnace or thelike having a wall, comprising, in combination, a radiant tube having aninlet leg and an outlet leg having a portion adapted to extend through awall of a furnace or the like; an axially extending burner co axial withthe axis of said inlet leg and adapted to have its inner end terminatesubstantially within the thickness of a wall, an axially extendingrecuperative heat exchanger tube coaxial with the axis of said outletleg and having a substantial part thereof within said portion of saidoutlet leg adapted to be within the thickness of a wall, said heatexchanger tube having an outlet for corn bustion air in an outer portionthereof and combustion air inlet means extending through an outerportion thereof, said heat exchanger tube having a closed inner end andadapted to separate said combustion air and exhaust gases and a pipeconnecting the interior of said heat exchanger tube with the interior ofsaid inlet leg adapted to be positioned outwardly of a wall to conductcombustion air heated by heat exchange with said exhaust gases to saidburner.

4. A recuperative radiant tube burner mechanism as set forth in claim 3in which the inner end of said combustion air inlet means terminatesadjacent but outwardly of said inner end of said heat exchanger tube,said heat exchanger tube is provided with longitudinally extending,radial fins for heat exchange and said pipe is provided with slidable,expandable seal means which are relatively gas-tight and respectivelyoperative at least during an operation of said mechanism.

5. A recuperative radiant tube burner mechanism [for a furnace or thelike, comprising, in combination, a conventional radiant tube having aninlet leg and an outlet leg, said legs having portions adapted to extendinto respective openings in a wall of a furnace or the like, a burnerhaving an axially extending fuel tube coaxial with said inlet leg, anaxially extending recuperative heat exchanger, extending into saidoutlet leg and spaced inwardly therefrom to provide a passage forexhaust gases along the outside of said heat exchanger, means forming anoutlet for combustion air in said heat exchanger, means forming acombustion air inlet in said heat exchanger in return bend relation tosaid outlet, said above-named means separating said inlet and outletfrom each other and -a pipe connecting the combustion air outlet of saidheat exchanger with said inlet leg to conduct combustion air heated byheat exchange with said exhaust gases to said burner.

6. In a furnace or the like, in combination, a member having an openingtherein with a cylindrical surface to receive the end of a pipe, a pipehaving a portion adapted to be slidably inserted in said opening forpassage therethrough of a heated fluid, said portion of said pipe havinga cylindrical outer surface opposed to said surface of said member, aperipheral recess in at least one of said surfaces and a plurality ofturns of temperature-expansible wire positioned in said peripheralrecess in retained relation thereto before assembly of said surfacesinto opposed position and normally projecting beyond said one of saidsurfaces, a distance substantially sufiicient substantially to extend attemperatures below elevated normal operating temperature of a furnace orthe like to the opposed surface without obstructing positioning of saidsurfaces, whereby a labyrinthine seal joint develops between said memberand said pipe at elevated temperatures.

7. A recuperative radiant tube burner mechanism for a furnace or thelike, comprising in combination a return bend radiant tube having aninlet leg and an outlet leg having portions adapted to extend intorespective passages through a wall of a furnace or the like, an axiallyextending burner having a fuel tube, mounting means to mount saidbln'ner on a furnace or the like with said fuel tube generally in axialregistry with the axis of and radially spaced from the inlet leg of thereturn bend radiant tube to provide an annular combustion air space forrecuperatively heated combustion air, an axially extending recuperatorhaving an inlet and an outlet for combustion' air, mounting means tomount said recuperator on a furnace or the like with said recuperatorgenerally in axial registry with the axis of the outlet leg of thereturn bend radiant tube, said recuperator being radially spaced by saidlast-mentioned mounting means from the inside of said outlet leg toprovide an exhaust gas space around said recuperator at least withinsaid portion of said outlet leg, means for conducting exhaust gases fromsaid out-let leg axially past said recuperator in heat exchange relationtherewith, and pipe means connecting said outlet for combustion air insaid recuperator with said combustion air space around said fuel tube tosupply recuperatively heated combustion air to said combustion airspace.

References Cited in the file of this patent UNITED STATES PATENTS292,537 Condit Jan. 29, 1884 2,226,816 Hepburn Dec. 31, 1940 2,462,395Heirnan Feb. 22, 1949 2,572,713 Plynt Oct. 23, 1951 2,602,440 Corns July8, 1952 2,700,380 Knight Jan. 25, 1955 2,796,118 Parker et a1. June 18,1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 3079 9lO March 5 1963 Frederick Sc Bloom et all,

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 2 line 62 for "exchange" read exchanger column 3 line 5 strikeout "opening first occurrence; line 41 for dispensnig" read dispensingline 73 after "inlet" insert we end column 5, line 32 after "exchanger",strike out the comma; column 6, line 7, after "surfaces" strike out thecomma; same column, line 14 for in combination read in combinationSigned and sealed this 1st day of October 19630 (SEAL) Attest:

ERNEST Wo SWIDER DAVID L. LADD Commissioner of Patents Attesting Officer

1. A RECUPERATIVE RADIANT TUBE BURNER MECHANISM FOR A FURNACE OR THELIKE, COMPRISING, IN COMBINATION, A RETURN BEND RADIANT TUBE HAVING ANINLET LEG AND AN OUTLET LEG HAVING PORTIONS ADAPTED TO EXTEND INRESPECTIVE PASSAGES THROUGH A WALL OF A FURNACE OR THE LIKE, A BURNERHAVING AN AXIALLY EXTENDING FUEL TUBE, MOUNTING MEANS TO MOUNT SAID FUELTUBE ON A FURNACE OR THE LIKE WITH SAID FUEL TUBE IN COAXIAL POSITIONRELATIVE TO THE INLET LEG OF THE RETURN BEND RADIANT TUBE, SAID MOUNTINGMEANS ADAPTED TO HOLD THE INNER END OF SAID BURNER SO AS TO TERMINATESUBSTANTIALLY WITHIN THE THICKNESS OF A WALL OF A FURNACE OR THE LIKE,SAID FUEL TUBE BEING RADIALLY SPACED BY SAID FIRSTNAMED MOUNTING MEANSFROM THE INSIDE OF SAID INLET LEG TO PROVIDE A HEATED COMBUSTION AIRSPACE AROUND SAID FUEL TUBE LEADING INTO SAID INLET LEG, AN AXIALLYEXTENDING RECUPERATOR HAVING AN INLET AND AN OUTLET FOR COMBUSTION AIR,MOUNTING MEANS TO MOUNT SAID RECUPERATOR ON A FURNACE OR THE LIKE WITHSAID RECUPERATOR IN COAXIAL POSITION RELATIVE TO THE OUTLET LEG OF SAIDRETURN BEND RADIANT TUBE, SAID LAST-MENTIONED MOUNTING MEANS ADAPTED TOHOLD THE INNER END OF SAID RECUPERATOR SUBSTANTIALLY WITHIN THAT PORTIONOF SAID OUTLET LEG ADAPTED TO BE